The risks posed by ultraviolet radiation have become noteworthy in recent years as concerns over environmental issues, particularly the thinning of the earth's protective ozone layer, increase. For instance, incidences of skin cancer due to overexposure to solar radiation and thus harmful ultraviolet rays have been on the rise. Ultraviolet (UV) radiation which has proven harmful to human skin includes the two different types known as UV-A, which falls within the range of 320-400 nm along the light spectrum, and UV-B, which is between 290-320 nm in wavelength. Any manner of reducing or preventing transmission of UV light thus must effectively block or absorb such radiation between these wavelengths (290 and 400 nm).
Ultraviolet radiation also affects the color of certain substrates by initiating degradation of dyes, colorants, pigments, and the like. Long-term exposure to direct sunlight eventually results in a loss of color or, at the least, a noticeable decrease in color strength. Such effects are particularly problematic within the automotive upholstery and drapery industries since the colored surfaces, car seats and curtains, are potentially exposed to ultra violet radiation for a great deal of time.
Sun protective compositions for direct contact with skin and colored surfaces have been developed in order to better prevent the damaging results from such overexposure. For instance, PABA, or para-aminobenzoic acid, is a popular UV blocking (or absorbing) compound which may be incorporated into a composition, such as a tanning lotion for skin, or a coating composition for car seats, and the like. This compound effectively absorbs the harmful radiation within the ultraviolet range of frequencies such that the user's skin or subject substrate is not fully exposed to such light. Recently, a new ultraviolet protective factor (UPF) test has been developed and adopted by the American Association of Textile Colorists and Chemists (AATCC) which provides a more thorough measurement of the ultraviolet absorption capabilities of specific fabrics within both the UV-A and UV-B wavelength ranges. This method, AATCC Test Method 183-1998 determines the ultraviolet radiation blocked or transmitted by textile fabrics intended to be used for UV protection. By utilizing a spectrophotometer or spectroradiometer, the UPF is calculated as the ratio of the erythemally (with erythema being the measurement of abnormal redness of skin due to ultraviolet radiation exposure) weighted ultraviolet radiation (UV-R) irradiance at the detector with no specimen present as compared to the UV-R irradiance with a specimen present, both over a range of wavelengths measured in intervals. This AATCC Test Method also measures Solar Spectral Irradiance through the subject fabric.
In order to decrease ultraviolet transmissions through clothing, past developments have provided protective measures from such harmful radiation through the introduction of certain compounds into or onto apparel fabrics. The prior art representative of this technology includes U.S. Pat. Nos. 4,857,305 to Bernhardt et al., 5,458,924 to Kashiwai et al., and 5,637,348 to Thompson et al, as well as United Kingdom Patent 889292 to American Cyanamid. Furthennore, certain types of weaves, twists, or bends of yarns or fabrics have been developed which effectively screen a wearer's skin from ultraviolet radiation. Such technology is represented within the prior art through U.S. Pat. No. 4,861,651 to Goldenhersh. With such chemically treated or physically modified fabrics, a wearer could then cover his or her skin more effectively solely through adorning themselves with such sun protective apparel. However, the prior art modified fabrics still permit transmission of relatively high levels of UV transmission and are expensive to produce. In order to decrease the potential color degradation for substrates due to ultra violet exposure, UV-absorbing copolymer latices have been utilized, most notably as films, coatings or adhesives. Such latices have provided, for example, a barrier to potentially damaging ultraviolet rays, both to a coated article and to, if such an article comprises apparel, a wearer of such an article. Polymer UV absorbing latices for textiles thus generally provide a beneficial, cost-effective protective alternative to higher density and higher costing fabrics.
Ultraviolet absorbing polymer latices incorporating UV-absorbing monomers and vinyl-functional comonomers have been disclosed within the prior art. However, nowhere has the novel procedure of emulsion polymerization of at least two monomers, all in the presence of a chain transfer agent, most notably 1-dodecanethiol, been taught, fairly suggested, or practiced. Past polymer UV absorbing latices include those taught within U.S. Pat. No. 5,629,365, to Razavi, entirely incorporated herein by reference. Such polymer latices comprise the same comonomers as in the instant, namely benzotriazole- and/or benzophenone-containing monomers polymerized with vinyl functional monomers; however, patentee both requires that the final product be subject to cross-linking, as is unnecessary within the inventive latex, and fails to mention or fairly suggest the presence of a chain transfer agent. Also of note as prior UV-absorbing polymer latices are those products taught within U.S. Pat. No. 4,528,111, to Beard et al., also herein entirely incorporated by reference. These polymers comprise the same benzotriazole comonomers as in the present invention; however, such latices are not formed of the same vinyl-functional comonomers, or through the same emulsion polymerization in the presence of a chain transfer agent as within the inventive latex. Patentee's latices are made through a solution polymerization process which includes the utilization of environmentally damaging solvents. Furthermore, the requisite solvents used within solution polymerization procedures are known to adversely affect subject substrates, particularly textiles, through dissolving dyes and colorants, hindering lightfastness by plasticizing finishes on textiles, and degrading polymer coatings. As a result, solution polymerization is an highly undesirable method of producing a stable polymer latex, again, particularly for textile substrates.
Other prior U.S. patents disclose similar compositions and procedures as those mentioned above; however, again, there is no prior teaching of the inventive process utilizing a chain transfer agent during an emulsion polymerization in order to form an UV-absorbing polymer latex. Such U.S. Patents which teach the polymerization of an UV-absorbing monomer with a vinyl functional comonomer include 3,429,852, to Skoultchi, 3,745,010, to Janssens et al., 3,761,272, to Mannens et al., 4,443,534, to Kojima et al., 4,455,368, to Kojima et al., 4,612,358, to Besecke et al., 4,652,656, to Besecke et al., 5,099,027, to Vogl et al., and 5,459,222, to Rodgers et al., all herein entirely incorporated by reference.
Even with all the previous work performed in this crowded area, there still remains a great need to produce a long-lasting, lightfast, stable, hard to remove, easily handled, and cost-effective ultra violet-absorbing polymer latex for application to certain surfaces in order to act as a barrier against potentially damaging penetrative UV rays.